Outboard pontoon semi-submersible offshore platform

ABSTRACT

An “outboard pontoon” semisubmersible floating platform for the use of offshore applications has a hull configuration including vertical deck support columns and a horizontally disposed pontoon structure. The vertical columns support the deck structure at upper ends and adjoin pontoon at their lower ends. Under the premise of ensuring platform stability, structural feasibility, and structural cost efficiency, the pontoon is horizontally extrapolated as far as possible radially outward from platform center in the horizontal plan while the elevation of the bottom of columns ranges anywhere from the pontoon bottom to the top surface of the pontoon. The vertical columns are adjoined to the pontoon from its inner periphery and the central vertical axis of each column resides a distance inward from the closest point of the center line of the pontoon. This arrangement makes part of pontoon become the “outboard pontoon” which is the important concept introduced by this invention. The “outboard pontoon” and the raised bottom elevation of the vertical columns will play an important role to reduce the vertical motion response of the platform to the sea waves, which has solid theoretical basis in hydrodynamics. Risers can be supported on the pontoon and columns, be extended to the deck, and the structure can be anchored by mooring lines extending along the outboard face of the outboard columns extending radially outward and downward from their lower ends.

BACKGROUND OF THE DISCLOSURE

The present invention relates generally to offshore floating vessels and platform structures used in the exploration and production of oil and gas products, particularly to an “outboard pontoon” semi-submersible offshore platform for installation and use in deep water offshore operations. This invention relates generally to floating offshore applications, including applications outside the offshore oil and gas industry.

Semi-submersible offshore platforms are connected to sub-sea wellheads and other installations via commonly referred to as risers or riser pipes. This invention functions to reduce the heave motion of the platform by an innovational arrangement of the relative position of pontoon and vertical columns. Improving platform heave motion performance is important on a semi-submersible platform design since it can reduce the strength damage and fatigue damage of platform structures and equipment and reduces overall system costs. Furthermore, better heave motion performance on semi-submersible platforms will reduce the risk and inconvenience in all types of offshore operations.

SUMMARY OF THE INVENTION

In accordance with the preferred embodiments of the present invention, it is therefore an objective of the present invention to provide an “outboard pontoon” semisubmersible floating platform for use in offshore applications having a hull configuration with vertical columns and a pontoon structure to improve its hydrodynamic performance through the innovational arrangement of the relative positions between pontoon and columns.

The arrangement is in such ways that the lower ends of the vertical columns are adjoined to the pontoon from the pontoon's inner periphery and the central vertical axis of each column is displaced in a distance inward from the adjacent pontoon center line. The pontoon is horizontally extrapolated as far as possible radially outward from the platform center in the horizontal plan to make part of the pontoon become an “outboard pontoon” for different wave incident directions.

The columns support the deck structure at their upper ends. The bottom elevation of the column can be placed in a range anywhere from the bottom of the pontoon to the upper surface level of the pontoon.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand in detail, the manner in which the above recited features, advantages, and objects of the present invention are attained, a more particular description of the invention briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.

It is noted, however, that the appended drawings show only typical embodiments of this invention and are therefore not to be considered as limiting of its scope, since the invention may admit to other equally effective embodiments.

FIG. 1 is a perspective view illustrating the first preferred embodiment of a semisubmersible platform of the present invention;

FIG. 2 is a side view of the semisubmersible platform shown in FIG. 1 ;

FIG. 3 is a top plan view of the semisubmersible platform shown in FIG. 1 ;

FIG. 4 and FIG. 5 are the top plan views illustrating the concept of “outboard pontoon” with different wave incident directions for the First preferred embodiment of a semisubmersible platform of the present invention;

FIG. 6 , FIG. 7 , and FIG. 8 are a perspective view, a side view and a top plan view respectively, illustrating the variations of the relative position of the pontoon and columns of the first preferred embodiment of a semisubmersible platform of the present invention;

FIG. 9 and FIG. 10 are a side view and a top plan view respectively, illustrating the Second preferred embodiment of a semisubmersible platform of the present invention;

FIG. 11 and FIG. 12 are the top plan views illustrating the concept of “outboard pontoon” for different wave incident directions for the Second preferred embodiment of a semisubmersible platform of the present invention;

FIG. 13 and FIG. 14 are a side view and a top plan view respectively, illustrating the Third preferred embodiment of a semisubmersible platform of the present invention;

FIG. 15 and FIG. 16 are the top plan views illustrating the concept of “outboard pontoon” for different wave incident directions for the Third preferred embodiment of a semisubmersible platform of the present invention;

FIG. 17 and FIG. 18 are a side view and a top plan view respectively, illustrating the Fourth preferred embodiment of a semisubmersible platform of the present invention;

FIG. 19 and FIG. 20 are the top plan views illustrating the concept of “outboard pontoon” for different wave incident directions for the Fourth preferred embodiment of a semisubmersible platform of the present invention;

FIG. 21 and FIG. 22 are a side view and a top plan view respectively, illustrating the Fifth preferred embodiment of a semisubmersible platform of the present invention.

FIG. 23 and FIG. 24 are the top plan views illustrating the concept of “outboard pontoon” for different wave incident directions for the Fifth preferred embodiment of a semisubmersible platform of the present invention;

FIG. 25 and FIG. 26 are a side view and a top plan view respectively, illustrating the Sixth preferred embodiment of a semisubmersible platform of the present invention.

FIG. 27 and FIG. 28 are the top plan views illustrating the concept of “outboard pontoon” for different wave incident directions for the Sixth preferred embodiment of a semisubmersible platform of the present invention;

FIG. 29 and FIG. 30 are a side view and a top plan view respectively, illustrating the Seventh preferred embodiment of a semisubmersible platform of the present invention.

FIG. 31 and FIG. 32 are the top plan views illustrating the concept of “outboard pontoon” for different wave incident directions for the Seventh preferred embodiment of a semisubmersible platform of the present invention;

FIG. 33 and FIG. 34 are a side view and a top plan view respectively, illustrating the Eighth preferred embodiment of a semisubmersible platform of the present invention.

FIG. 35 and FIG. 36 are the top plan views illustrating the concept of “outboard pontoon” for different wave incident directions for the Eighth preferred embodiment of a semisubmersible platform of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The First preferred embodiment of a semisubmersible platform in accordance with the present invention is generally identified by FIG. 1 through FIG. 3 , which are a perspective view, a side view and a top plan view of the embodiment, respectively. The platform includes four columns (11) having upper ends (11C) above the water surface (14) for engaging and supporting a platform deck (10) thereon. Horizontally disposed pontoons (12) have circular profiles which are connected to the bottom of column 11 (11A) by auxiliary supporting structures 13A and 13B. The auxiliary supporting structures 13A and 13B shown herein are for illustrative purposes only and the concrete design should be determined according to the needs. The arrangement of columns 11 is in such way that outer sidewalls 11B of columns 11 is in-line with inner sidewall 12B of pontoon 12 while the bottoms (11C) of columns 11 have the same elevation as that of pontoon 12's top surface (12A). There is an extension 13 of each column 11 at the bottom portion extended into pontoon 12 to form an internal access from each column 11 to pontoon 12. This arrangement makes the section center (11D) of each column deviate inwardly from the center line of pontoon 12C and makes part of pontoon 12 become “outboard pontoon”, which is the key concept proposed in this invention.

FIG. 4 illustrates the concept of “outboard pontoon” of the First preferred embodiment of a semisubmersible platform of this invention. The definition of “outboard pontoon” is as following: for the given incident wave direction, drawing a line (16) perpendicular to the wave direction and passing through the section center of up-wave column(s) 11E, and drawing anther line (17) parallel to line 16 and passing through the section center of down-wave column(s) 11F, the portion of the pontoon outside line 16 and 17 is called the “outboard pontoon” (12D) while the portion of the pontoon between these two lines can be called “inboard pontoon” (12E). Generally, the larger the “outboard pontoon” is, the farther away it is from center of the platform and the better heave motion performance the platform has. The distance between section center 11D of column 11 and center line 12C of the pontoon is labeled as 15 in FIG. 3 . It is obvious that increasing this distance (15) is favorable in terms of heave motion response.

FIG. 5 illustrates the concept of “outboard pontoon” in the First preferred embodiment of a semisubmersible platform of this invention for another wave direction. The portion of “outboard pontoon” in FIG. 5 is smaller than that of FIG. 4 . But in FIG. 5 , the two columns 11G are in the middle of line 16 and line 17 and will compensate the influence of the reduction of “outboard pontoon” and maintain the heave motion performance.

The circular pontoon profile and the deviation of the center of column inward from the pontoon middle circle, which enlarge the “outboard pontoon”, along with the raised bottom elevation of columns to the top surface of the pontoon, are the two key factors to improve the heave motion of the platform in the First preferred embodiment of a semisubmersible platform of present invention.

FIG. 6 through FIG. 8 present a perspective view, a side view, and a top plan view of an alternation of the First preferred embodiment shown in FIG. 1 through FIG. 3 , respectively. It can be seen from FIG. 6 through FIG. 8 that the columns (11) are partially imbedded into pontoon (12) horizontally from the pontoon inner sidewall 12B, and vertically from pontoon top surface 12A. The alternative design is mainly to reduce the complexity and increase the reliability of the structural design in the connections of columns 11 to the pontoon 12. It is also to reduce the overall dimension of the hull structure in the horizontal plan which, sometimes, is important in the hull fabrication. The auxiliary supporting structures such as 13A and 13B shall be used as needed.

FIG. 9 through FIG. 36 illustrate other seven preferred embodiments of the current invention. Please note the basic ideas of these seven preferred embodiments are the same as those in the first preferred embodiments, but only the scenarios in which columns partially imbedded into pontoon are presented.

FIG. 9 and FIG. 10 are a side view and a top plan view respectively, illustrating the Second preferred embodiment of a semisubmersible platform of the present invention. The profile of ring-pontoon 12 is in the form of rounded square. The four columns (11) with rounded square cross-sections are disposed in the middle of each pontoon side and partially imbedded into the pontoon horizontally from inner side wall 12B of pontoon 12 and vertically from top surface 12A of pontoon 12. This arrangement will create substantial “outboard pontoon” as shown in FIG. 11 and FIG. 12 to improve heave motion performance of the platform. As mentioned previously, the auxiliary supporting structures 13A and 13B shall be used as needed.

FIG. 13 and FIG. 14 are a side view and a top plan view respectively, illustrating the Third preferred embodiment of a semisubmersible platform of the present invention. The profile of ring-pontoon 12 is in the form of a rounded square. The four columns (11) with a rounded square cross-section are disposed in the middle of each pontoon side and partially imbedded into the pontoon horizontally from inner side wall 12B of pontoon 12 and vertically from top surface 12A of pontoon 12. This arrangement will create substantial “outboard pontoon” as shown in FIG. 15 and FIG. 16 to improve heave motion performance of the platform. As shown in above figures, the third preferred embodiment can be obtained from the Second preferred embodiment by rotating each column in the Second preferred embodiment about its vertical axis 45 degrees. This arrangement is to reduce the sensitivity of platform response to the current direction. As mentioned previously, the auxiliary supporting structures 13A and 13B shall be used as needed. This statement applies to all preferred embodiments presented in this invention and will not be shown in the rest of pictures hereafter.

FIG. 17 and FIG. 18 are a side view and a top plan view respectively, illustrating the Fourth preferred embodiment of a semisubmersible platform of the present invention. The profile of ring-pontoon 12 is in the form of rounded triangle. The three columns (11) with rounded circular cross-section are disposed in the middle of each pontoon edge and partially imbedded into the pontoon horizontally from its inner side wall 12B and vertically from its top surface 12A. This arrangement will create substantial “outboard pontoon” as shown in FIG. 19 and FIG. 20 to improve heave motion performance of the platform.

FIG. 21 and FIG. 22 are a side view and a top plan view respectively, illustrating the Fifth preferred embodiment of a semisubmersible platform of the present invention. The profile of ring-pontoon 12 is basically square but has an extension on both ends of each side. The four columns (11) with rounded square cross-sections are disposed in each Conner of the pontoon square and imbedded partially into the pontoon horizontally from inner side wall 12B of pontoon 12 and vertically from top surface 12A of pontoon 12. This arrangement will create substantial “outboard pontoon” as shown in FIG. 23 and FIG. 24 to improve heave motion performance of the platform.

FIG. 25 and FIG. 26 are a side view and a top plan view respectively, illustrating the Sixth preferred embodiment of a semisubmersible platform of the present invention. The profile of ring-pontoon 12 is the same as that of the Fifth preferred embodiment of this invention. The only difference is the orientation of the four rounded square column at horizontal plan. As shown in the figures, the sixth preferred embodiment can be acquired from the Fifth preferred embodiment by rotating each column in the Fifth preferred embodiment 45 degrees about its vertical axis. This arrangement is to reduce the sensitivity of platform response to the current direction. The “outboard pontoon” shown in FIG. 27 and FIG. 28 is similar as that in FIG. 23 and FIG. 24 .

FIG. 29 and FIG. 30 are a side view and a top plan view respectively, illustrating the Seventh preferred embodiment of a semisubmersible platform of the present invention. The profile of ring-pontoon 12 is basically square but has extensions in each corner of the square pontoon in the direction of the 45-degree bisector of each quadrant away from the center of the platform. The four columns (11) with rounded square cross-sections are disposed in the four pontoon corners and partially imbedded into the pontoon horizontally from its inner side wall 12B and vertically from its top surface 12A of pontoon 12. This arrangement will create substantial “outboard pontoon” as shown in FIG. 3 land FIG. 32 to improve heave motion performance of the platform.

FIG. 33 and FIG. 34 are a side view and a top plan view respectively, illustrating the eighth preferred embodiment of a semisubmersible platform of the present invention. The profile of ring-pontoon 12 is the same as that of the seventh preferred embodiment of this invention. The only difference is the orientation of the four rounded square columns at the horizontal plan. As shown in the figures, the Eighth preferred embodiment can be developed from the Seventh preferred embodiment by rotating each column in the Seventh preferred embodiment 45 degrees about its vertical axis. This arrangement may reduce the sensitivity of platform response to the current direction. The “outboard pontoon” is shown in FIG. 35 and FIG. 36 similar to that in FIG. 31 and FIG. 32 . 

What is claimed is:
 1. It will be observed in the eight preferred embodiments that the columns (11) are depicted as substantially square/rounded square or circular members and the pontoon-ring (12) configuration is depicted as substantially circular, rounded triangle, rounded square or square with extension. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms and not intended to be limiting. While eight preferred embodiments of the invention have been shown and described, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims which follows:
 1. An “outboard pontoon” semisubmersible floating platform, comprising of: a) a horizontal pontoon connected by the bottom of columns with auxiliary reinforcing structures as needed to form a sustainable pontoon-ring. The said pontoon-ring is horizontally extrapolated as far as possible radially outward from the center of the platform in the horizontal plan to form parts of the pontoon-ring as the “outboard pontoon” as illustrated in these eight preferred embodiments; b) at least three support columns that extend upwards from their bottom parts where the pontoon ring is connected, and a deck which is supported by the columns above the water surface on the upper ends of said columns. The bottom elevation of said columns can ranged from the pontoon-ring's bottom elevation to the pontoon ring's top surface elevation. While the preferred elevation of the bottom of the column is at the same elevation of the pontoon's top surface, other elevations within the range may be used as well depending on circumstances. c) Vertical columns in which said column's lower ends are adjoined to the pontoon's inner ring. And, there exists a distance between the central vertical axis of each column and the closest center line of the pontoon. The bottom portion of said columns may be partially imbedded into said pontoon-ring as illustrated as in the preferred embodiments for the safety and convenience of structural design and for the reduction of overall dimension in the horizontal direction of the platform.
 2. The platform of claim 1 where said pontoon-ring may have the horizontal cross-section of, but not limiting to, a circular, rounded triangular, rounded square or other polygon form, or have extended portions as illustrated in the preferred embodiments.
 3. The platform of claim 1, wherein said columns have at least three of them. The number of said columns may be four, five, six, seven or eight that have the same features as claimed in the claim 1 and distributed along said pontoon-ring.
 4. The platform of claim 1, wherein said columns have horizontal cross-sections of, but not limited to, circular, square/rounded square, rectangular/rounded rectangular or other forms of polygons. 